Federal police on a vehicle guard one of the three forensic trucks where several bodies were placed after dozens of bodies, some of them mutilated, were found on a highway connecting the northern Mexican metropolis of Monterrey to the U.S. border found in the town of San Juan near the city of Monterrey, Mexico, Sunday, May 13, 2012. (AP Photo/Christian Palma)

Photo By JULIO CESAR AGUILAR

Mexican Federal personnel police block the road between the cities of Monterrey and Reynosa, Mexico, (in the border with the USA), on May 13, 2012. At least 37 mutilated bodies were found the road in the North of Mexico, surrounding the metropolitan area of Monterrey, the third most populated in the country, the State Prosecutor's Office reported AFP PHOTO/JULIO CESAR AGUILARJulio Cesar Aguilar/AFP/GettyImages

Photo By Christian Palma

Forensic experts examine the area where dozens of bodies, some of them mutilated, were found on a highway connecting the northern Mexican metropolis of Monterrey to the U.S. border in the town of San Juan near the city of Monterrey, Mexico, Sunday, May 13, 2012. (AP Photo/Christian Palma)

Photo By Christian Palma

Federal police on a vehicle guard one of the three forensic trucks where several bodies were placed after dozens of bodies, some of them mutilated, were found on a highway connecting the northern Mexican metropolis of Monterrey to the U.S. border found in the Km 47 of the Reynosa-Cadereyta road in the town of San Juan near the city of Monterrey, Mexico, Sunday, May 13, 2012. (AP Photo/Christian Palma)

More Information

Escalating violence

Some notable incidents of mass violence in Mexico's drug war over the past year:

» Sunday: Mutilated bodies of 49 people dumped on highway in northern Mexico.

» Aug. 25: Gunmen burst into casino in Monterrey, douse it with gasoline and start fire that kills 53 people.

» July 8: At least 20 people killed when gunmen open fire at bar in Monterrey. Eleven bodies shot with high-powered rifles found piled near well on outskirts of Mexico City.

» June 7: Federal officials announce finding 193 corpses in recent months buried in town of San Fernando in Tamaulipas state, most of them migrants kidnapped off buses and killed by Zetas.

Associated Press

MEXICO CITY - Officials blamed the Zetas gang for the slaughter of 49 people whose headless, handless bodies were recovered early Sunday near a highway that leads from the industrial city of Monterrey to the South Texas border.

A message left with the bodies outside the oil refining town of Cadereyta - supposedly signed by the Zetas - claimed credit for the latest in a series of recent atrocities by rival criminal gangs waging a brutal terror campaign against one another. The message's content was not disclosed.

Though the lack of heads or fingerprints obviously will complicate identification of the victims, authorities rushed to assure a beleaguered public that ordinary citizens aren't being targeted.

"This is not an attack against the civilian population," Jorge Domene, public security spokesman for the state of Nuevo Leon, said at a news conference. "That's important to point out."

The corpses of the 43 men and six women were dumped about 2 a.m. The victims were killed elsewhere as many as two days ago, Domene said.

Monterrey and its suburbs, home to some 4 million people, have become a crucial front of the gangland violence that has killed more than 50,000 people since President Felipe Calderon deployed federal forces against Mexico's powerful gangs upon taking office in December 2006.

The escalating bloodshed has besieged Cadereyta and nearby towns in recent months as the Zetas battle their former paymasters from the Gulf Cartel for regional dominance. Both narcotics trafficking gangs are anchored in the Mexican cities bordering south Texas.

Thriving drug trade

In addition to its own local narcotics market, metropolitan Monterrey is an important warehousing center for cocaine, marijuana and other illegal drugs bound for U.S. consumers. Petroleum pipelines running between Cadereyta and the border have also been among those most tapped by thieves, supplying Mexico's vibrant black market for gasoline and other petroleum products. Small towns, ranches and isolated clusters of weekend houses between Monterrey and the border long have been favored haunts for gangsters.

Fighting in the Monterrey area and along the border recently has worsened with the participation of gunmen loyal to Joaquin "El Chapo" Guzman, the crime boss based in the Pacific Coast state of Sinaloa. Considered Mexico's most powerful gangster, Guzman reportedly has allied with the Gulf Cartel and returned to the region - especially to Nuevo Laredo - to take on the Zetas.

Sunday's slaughter followed the murder last week of 18 people near the western city of Guadalajara - at least some of them apparent innocents kidnapped from once-bucolic towns where thousands of U.S. and Canadian retirees live. Officials also have blamed the Zetas for those killings, which supposedly were committed in response to the Guzman gang's killing in the past month of dozens of alleged Zetas in Nuevo Laredo.

In response, Calderon's government has extended cooperative security agreements with both Nuevo Leon and Tamaulipas states - which border Texas from upriver of Laredo to the Gulf of Mexico - to guarantee the continued presence of federal troops and police.

"We are not going to yield, we will never yield," Nuevo Leon Gov. Rodrigo Medina said in signing the agreement Thursday in Monterrey. "We will continue investing and taking the necessary actions so that Nuevo Leon has solid institutions and safe cities."

Zetas inmates aided by guards murdered 44 other prisoners allegedly belonging to the Gulf Cartel in the state prison in Apodaca, another Monterrey suburb in mid-February. More than 30 of the Zetas prisoners then slipped over the jail walls. The prison's new warden, named just three weeks ago, resigned Sunday citing "personal reasons."

New tactic

Intended to terrorize rivals and the general population, the public display of butchered corpses has replaced the traditional gangland practice of burying victims in clandestine mass graves. Hundreds of bodies were collected from such graves last year in both northeastern Mexico and the western state of Durango.

But in September killers allied with Guzman dumped 35 bodies of accused Zetas on an highway interchange near an upscale suburban mall in the port of Veracruz. Zetas and their allies responded in November by leaving 26 corpses, supposedly belonging to members of Guzman's Sinaloa Cartel, in downtown Guadalajara. The Zetas also claimed the massacre of several dozen people in Sinaloa this spring.

"I have no doubt that this is a media measure taken by organized crime to get the attention of the public and the rival group," Javier del Real, the retired army general who was recently appointed head of Nuevo Leon's state police, said of the Cadereyta incident at Sunday's news conference. "They achieved that result."